1. Field of the Invention
The present invention relates generally to image forming apparatuses and drive-voltage generating circuits.
2. Description of the Related Art
Conventionally, an inkjet printer that uses a piezoelectric element as an actuator apply a voltage waveform that is called a drive waveform to the piezoelectric element so as to control a droplet size and an discharging speed of an ink droplet. The maximum value of an electric current supplied to the piezoelectric element increases when the piezoelectric element has a large capacitive load, when a voltage fluctuation width of the drive waveform has increased, or when a slew rate of the drive waveform is steep. Accordingly, a drive-waveform generating circuit is required to correspond to a high-current output.
Known circuit configurations for corresponding to the high-current output include a configuration in which each transistor included therein is changed to that of a higher rated current and a configuration in which a plurality of amplifier circuits is arranged in parallel with each other so as to disperse current loads among the amplifier circuits.
Disclosed in Japanese Patent Laid-open Publication No. 2006-088695 is an apparatus that includes a plurality of drive-waveform generating circuits for a purpose of preventing overloading a voltage-waveform generating circuit. That is, the apparatus controls as to which one of the drive-waveform generating circuits supplies a drive waveform to which one of the piezoelectric elements so that a load on each of the drive-waveform generating circuits remains within a predetermined level.
However, there remain problems in the conventional circuit configurations. For instance, when transistors in the configuration are replaced with high rated current transistors, a frequency response characteristic decreases, so that a steep drive waveform cannot be output. When a load in the configuration is dispersed to a plurality of drive circuits, concentration of the load on some particular circuits may occur; accordingly, low rated transistors cannot be used, making the production cost of the configuration to be high. A technique such as that disclosed in Japanese Patent Laid-open Publication No. 2006-088695 can result in an increase in cost because of an additional component and an increase in complexity of a circuit related to the addition of a switching circuit for controlling signals necessary for controlling a load balance.
Therefore, there is a need for providing an image forming apparatus and a drive-voltage generating circuit in which a current amplifying circuit for driving an actuator, which is implemented by using a capacitive load, in the image forming apparatus does not include high-rated-current (costly) components but has a required characteristic and is configured by components with a small parts count.